1. Field of the Invention
The present invention relates to a method and related communication device used in a wireless communication system and more particularly, to a method for transfer capability information related to an evolved third generation wireless communications system in a second generation wireless communications system and related communication device.
2. Description of the Prior Art
Global system for mobile communication (GSM) is a globally accepted second generation (2G) standard for digital cellular communication. A GSM network includes a switching system (SS), a base station system (BSS), and an operation and support system (OSS). A mobile switching center, part of the SS, performs the telephony switching functions of the system, e.g. an inter-RAT (Radio Access Technology) handover. The BSS handles a radio interface to a mobile station (MS) and provides physical links and related control functions with the MSC.
With evolution of the telecommunication system, a long term evolution system is developed as an evolved third generation (3G) standard to provide a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of user equipments (UEs).
Due to demand for a multi-mode device, the MS can support the LTE system in addition to the GSM system, and is stored with capability information of each supported system. The capability information mainly associates with abilities of link establishment, measurement, frequency tuning, etc. When the MS operates in the GSM system, the GSM network can initiate an inter-RAT to the E-UTRAN for the MS. The GSM network and the E-UTRAN need to know how much EUTRA capability (the capability associates with the LTE system) the MS has, so as to generate a handover message for configuring the MS during the inter-RAT. With handover configuration appropriately set based on the EUTRA capability information, the MS is able to successfully connect the E-UTRAN; otherwise the inter-RAT is failed.
However, the prior art does not provide a way for the MS in the GSM system to transmit the EUTRA capability information to the GSM network responsible for transferring the MS capabilities to the E-UTRAN. Without the EUTRA capability information, the GSM network cannot arrange Inter-RAT handover to EUTRAN for the UE. Then the UE cannot get higher-QoS (Quality of Service) service provided by the E-UTRAN even if the UE is under EUTRAN coverage.